U.S. Pat. Nos. 1,368,413 and 1,596,751 disclose tube rolling machines or shear forming apparatus wherein a metal tube is fed through a set of shear forming rollers which are orbited around the tube for reducing the outside diameter of the tube by either reducing the wall thickness of the tube and/or by also reducing the inside diameter of the tube. The metal tube may be fed through the orbiting shear forming wheels by locating the axis of each wheel askewed relative to the axis of the tube, for example, as disclosed in above-mentioned U.S. Pat. No. 1,368,413. The tube may also be fed through the wheels by pulling the tube with a carriage mounted for movement along an elongated track. In one machine, the carriage was moved along the track by a lead screw in a manner similar to the movement of a carriage along the bed of a metal cutting lathe.
In shear forming apparatus of the general type described above, it is desirable to provide means for moving the shear forming wheels in corresponding radial directions while the wheels are orbiting around the tube in order to reduce the outside diameter of the metal tube. The inside diameter of the tube may be predetermined by selecting the diameter of a mandrel which is located within the tube in the zone of the orbiting forming wheels, for example, as disclosed above-mentioned U.S. Pat. No. 1,368,413. The inner limits of radial movement of the forming wheels may be selected by providing each wheel holder with a screw which may be adjusted when the wheel support head is stopped. However, it is highly desirable to provide means by which the inner limits of radial movement of the forming wheels may be simultaneously and precisely adjusted while the wheel support head is rotating so that the finished outside diameter of the metal tube may be quickly and precisely selected without stopping the head and thereby provide the shear forming apparatus with a high efficiency in the production of tubes with reduced precision diameters.